(1) Field of the Invention
The present invention relates to a magneto-optical recording element. More particularly, the present invention relates to a magneto-optical recording element which is suitable for the magnetic field modulation recording method and makes overwriting possible.
(2) Description of the Prior Art
Magneto-optical recording using an amorphous metal alloy comprising a rare earth metal element and a transition metal element has been vigorously studied. According to this recording method, convergent laser beams are projected on a recording medium to effect local heating and writing of bits and the bits are read out by utilizing the magnetic-optical effect. Furthermore, the recorded bits can be erased and new bits can be written again.
In the case where rewriting is performed according to the light power modulation method, recording and erasure should be separately carried out, and hence, a magneto-optical disk should be turned at least two times. Accordingly, real-time rewriting is impossible.
Use of the magnetic field modulation recording method for rewriting instead of this light power modulation recording method has been proposed. According to this method, overwriting is possible, but it is necessary to use a magnetic head capable of high-speed switching under application of a large bias magnetic field. Since this magnetic head has a large driving current and a large reactance, fabrication of this magnetic head is difficult.
In this magnetic field modulation recording method, a magnetic material in which recording can be performed by a small external magnetic field is desired, and recently, a TbFeCo magnetic alloy in which the rare earth element-sub-lattice moments are dominant at room temperature and which has the compensation temperature between the Curie temperature and room temperature has been proposed as the material satisfying this desire. It is reported that if this magnetic alloy is used, recording is possible at about .+-. 200 Oe.
In U.S. Pat. No. 4,751,142, we proposed use of a perpendicular magnetization film composed of an alloy having a composition represented by the formula (Gd.sub.y Dy.sub.1-y).sub.x Fe.sub.1-x in which .times. is a number of from 0.15 to 0.35 and y is a number of from 0.30 to 0.95. Furthermore, U.S. Pat. No. 4,680,742 teaches that a deposition layer of a composition comprising Si.sub.3 N.sub.4 and a refractive indeximproving agent such as Al.sub.2 O.sub.3 or Y.sub.2 O.sub.3 is used as the dielectric layer of a magneto-optical recording element.
However, a relative large bias magnetic field is necessary for the known magneto-optical recording elements, and development of an element capable of recording at a magnetic field intensity lower than .+-. 200 Oe, especially lower than .+-. 150 Oe, is desired.